Flow restrictor-separation device

ABSTRACT

A method of partitioning a pre-selected phase of a sample of liquid having a plurality of phases of differing densities, a separation device and a tube containing the separation device. The sample of liquid is placed in a first chamber of a linear tube that is separated from a second chamber by a separation device. The separation device slidably engages the interior surface of the tube in an essentially fluid-tight manner and has an axial orifice on the longitudinal axis of the tube that is in fluid flow communication with a flow-restriction channel. The phases are ordered concentrically by rotating the tube around its longitudinal axis e.g. in an axial centrifuge. The volume of the first chamber is reduced by movement of the separation device within the tube, that phase of the liquid located axially within the first chamber flowing into the axial orifice and passing through the flow-restriction channel into the second chamber. The reduction of the volume of the first chamber is controlled using phase-separation information. The method is useful in separation of blood components.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for theseparation into phases of a sample of liquid, including colloidalsuspensions, having a plurality of phases of differing densities, andfor the separation and maintaining of the separation of one phase of theliquid sample from the remainder of the liquid. The invention isparticularly useful in the separation of blood into components thereof,especially for purposes of testing and analysis of blood components.

The liquid to be separated is contained in a chamber, typically a tube,containing a separation device. The chamber is rotated, either axiallyi.e. about its longitudinal axis, or in a conventional centrifuge i.e.about an axis perpendicular to the longitudinal axis, to cause theliquid to separate into distinct phases, during which rotation aseparation device is moved through the liquid to physically separate atleast one of the phases. The separation device maintains the separationat the conclusion of the rotation and through subsequent handling steps.

BACKGROUND OF THE INVENTION

Diagnostic tests frequently require separation of a patient's wholeblood sample into components, especially cellular portions fromnon-cellular portions e.g. serum or plasma from cells. For instance,plasma is obtained from anticoagulated blood and still contains all ofthe coagulation proteins, whereas serum is obtained from clotted bloodwith the bulk of the coagulation proteins being retained with the clotand red blood cells. Samples of whole blood are typically collected byventipuncture through a special cannula or needle attached to a syringeor an evacuated collection tube. The sample of blood in the form that isto be separated into components is typically drawn, using a needle,through a penetrable self-sealing elastomeric closure or other stopperinto an evacuated tube. Separation is then accomplished, e.g. byrotation of the tube in a conventional centrifuge e.g. a swinging bucketor a fixed angle centrifuge, as the different components of the wholeblood have different densities, as described in U.S. Pat. No. 4 152 269of A. L. Babson.

It is frequently desirable to physically isolate the separated phasesfrom each other, so that separation of the phases is maintained aftercentrifugal rotation has ceased. Isolation may be accomplished byinterposing a gel material between the phases, the gel materialtypically being a silicone that is placed in the tube at the time ofmanufacture. These gels have densities that are intermediate those ofthe phases being separated and become interposed between the phasesduring centrifugal rotation, as is described in U.S. Pat. No. 4 350 593of Kessler and U.S. Pat. Nos. 3 852 194 and 4 083 784 of A. R. Zine.However, the gels may contain absorbed substances that can interferewith blood analyses or adsorb specific compounds from the blood e.g.tricyclic drugs, the separation of plasma or serum from blood cells maybe incomplete and severe jarring or shaking e.g. as in shipping ofsamples, may disrupt the seal and result in interaction of the separatedphases.

U.S. Pat. No. 3 929 646 of S. L. Adler describes a serum separator foruse in a centrifuge separation system. The separator is initiallypositioned at one end of a tube, adjacent to a tube stopper, with thewhole blood sample being contained within the tube. When the tube issubjected to centrifugal force, the separator moves away from thestopper and towards the other end of the tube. The separator is designedso as to have a density that is between the densities of two phases ofblood, so that when centrifugation is complete, it is positioned betweenthe two phases. The separator has openings to allow the lighter phase ofthe blood to pass through the separator and allow the separator to movethrough the blood sample. Thus, a blood sample can be separated intoplasma and cell phases that are physically separated. However, theopenings may become plugged with clotted blood fractions or converselypermit migration between phases when there is no centrifugal force; ineither event effective separation will be lost.

An apparatus and method of separating blood phases by rotation of a tubeabout its longitudinal axis i.e. axial rotation, are described in U.S.Pat. No. 4 828 716 of J. A. McEwen et al. The blood sample is introducedto the tube through a cap assembly that consists of a pierceable closureand a separator that has a one-way valve. The tube is then rotated aboutits longitudinal axis; the heavier cellular phase lines the tube walland thereby separates from the lighter non-cellular (plasma or serum)phase. Once separation has been achieved, an axial probe penetrates thepierceable closure, detaches the separator from the closure and forcesthe separator down the tube. The axially-located non-cellular phasepasses through the separator. An optical sensor is utilized to detectwhen the cellular phase begins passing into the separator, and to stopmovement of the separator. Thus, the two phases are physicallyseparated. However, it is believed that a separator that is morereliable in operation and which may be manufactured in a cost effectivemanner is required.

A related application of R. P. Luoma filed concurrently herewith isdirected to so-called double ended tubes.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method of partitioning apre-selected phase of a sample of liquid having a plurality of phases ofdiffering densities, comprising the steps of:

(a) containing said sample of liquid in a first chamber of a lineartube, said tube having a second chamber that is separated from the firstchamber by a separation device, said second chamber being free of theliquid, said separation device slidably engaging the interior surface ofthe tube in an essentially fluid-tight manner and having an axialorifice on the longitudinal axis of the tube that is in fluid flowcommunication with a flow-restriction channel, said flow-restrictionchannel being off-set from the longitudinal axis of the tube, saidflow-restriction channel having a convoluted path with at least twoaxially-oriented sections with opposed directions of fluid flow, saidaxial orifice being in fluid flow communication with the first chamberand said flow-restriction channel being in fluid flow communication withthe second chamber;

(b) ordering the phases of the sample concentrically by rotating thetube around its longitudinal axis;

(c) while the phases are ordered, reducing the volume of the firstchamber by movement of the separation device within the tube, that phaseof the liquid located axially within the first chamber flowing into theaxial orifice and passing through the flow-restriction channel into thesecond chamber; and

(d) deriving phase-separation information from the location of theinterface between the phases and controlling the reduction of the volumeof the first chamber on the basis of the phase-separation information.

In a preferred embodiment of the method of the invention, theflow-restriction channel permits flow of liquid from the first chamberto the second chamber during step (c) but restricts flow of liquid atother times.

In another embodiment, the second chamber is formed as the separationdevice is moved within the tube.

The present invention additionally provides a method of partitioning apre-selected phase of a sample of liquid having a plurality of phases ofdiffering densities, comprising the steps of:

(a) containing said sample of liquid in a first chamber of a lineartube, said tube having a second chamber that is separated from the firstchamber by a separation device, said second chamber being free of theliquid, said separation device slidably engaging the interior surface ofthe tube in an essentially fluid-tight manner and having an axialorifice on the longitudinal axis of the tube that is in fluid flowcommunication with a flow-restriction channel, said flow-restrictionchannel being off-set from the longitudinal axis of the tube, saidflow-restriction channel having a convoluted path with at least twoaxially-oriented sections with opposed directions of fluid flow, saidaxial orifice being in fluid flow communication with the first chamberand said flow-restriction channel being in fluid flow communication withthe second chamber; and

(b) ordering the phases of the sample by subjecting the tube tocentrifugal force.

The present invention also provides a separation device adapted toslidably engage the interior surface of a chamber in a linear tube in anessentially fluid-tight manner, said separation device having an axialorifice on the longitudinal axis thereof in fluid flow communicationwith a flow-restriction channel, said flow-restriction channel beingoff-set from the longitudinal axis of the separation device, saidflow-restriction channel having a convoluted path with at least twoaxially-oriented sections with opposed directions of fluid flow, saidaxial orifice and said flow-restriction channel providing fluid flowcommunication between a first side of the separation device and a secondside of the separation device.

In addition, the present invention provides a tube having a sealableopening on at least one end and a separation device located within thetube, said separation device separating a first chamber from a secondchamber within said tube, said separation device slidably engaging theinterior surface of the tube in an essentially fluid-tight manner andhaving an axial orifice on the longitudinal axis of the tube in fluidflow communication with a flow-restriction channel, saidflow-restriction channel being off-set from the axis of the tube andhaving a convoluted path with at least two axially-oriented sectionswith opposed directions of fluid flow, said axial orifice being in fluidflow communication with the first chamber and said flow-restrictionchannel being in fluid flow communication with the second chamber, saidtube and separation device providing means to insert liquid into thefirst chamber.

In embodiments of the invention, the flow-restriction channel is asingle continuous channel, especially a single continuous channel thatsubstantially encircles the longitudinal axis of the tube.

In other embodiments of the invention, the convoluted path conforms tothe surface of a cone.

In further embodiments of the invention, the second chamber is anincipient chamber that forms as the separation device is moved along thetube.

DESCRIPTION OF THE DRAWINGS

The invention will be described with particular reference to thedrawings in which: FIG. 1 is a schematic representation of across-sectional area of one embodiment of the separation device in atube; FIG. 2 is a schematic representation of a cross-sectional area ofanother embodiment of the separation device in a tube; FIG. 3 is aschematic representation of a cross-sectional area of a separationdevice; FIG. 4 is a schematic representation of a plan view of atortuous path in the separation device; FIG. 5 is a schematicrepresentation of a section of a separation device taken through line5--5 of FIG. 4; FIG. 6 is a schematic representation of a section ofanother embodiment of a separation device; and FIG. 7 is a schematicrepresentation of an exploded view of the separation device of FIG. 6.

The embodiments shown in FIG. 3 and FIG. 4 particularly relate to theembodiment shown in FIG. 1. Similarly, the embodiments shown in FIG. 6and FIG. 7 particularly relate to the embodiment shown in FIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1, tube 10 (which may also be known as or referred toas a vial) is shown as having a first end cap 11 and a second end cap12. As shown, the end caps are of different construction. Tube 10 has asubstantially constant diameter, and constant cross-section, throughouta major portion of its length. First end cap 11 is comprised of a plug13 having recess 14. Plug 13 fits inside tube 10 and forms a fluid andvacuum tight seal with the inner surface 15 of tube 10, so as to form afluid tight closure with tube 10. First end cap 11 also has rim 17 thatfits tightly onto the outside of tube 10. In addition, the exposed endof first end cap 11 is shown as having a flat end, which could be usedto stand the tube in a vertical position. In contrast, second end cap 12is shown as having a rounded exposed end. The shape of the end of endcaps 11 and 12 is not critical to the invention; the material ofconstruction is more important, as will become apparent, for penetrationof needles and probes during use of the tubes.

Second end cap 12 is shown as having recess 16, which is axially locatedin the end cap. In addition, second end cap 12 has rims 18 which fitover the end of tube 10 to form a fluid and gas tight seal therewith. Itwill be appreciated that there are variations in the type of end capthat may be used. In embodiments, the end cap is accompanied by astopper or plug, with the stopper or plug providing the fluid and gastight seal and the end cap being for protection and/or to retain thestopper or plug in place.

The separation device in tube 10 is generally indicated by 19.Separation device 19 divides the space within tube 10 into first chamber20 and second chamber 21; it is to be understood that in embodiments ofthe invention, end cap 12 contacts and seats with separation device 19such that second chamber 21 is in effect an incipient chamber whichforms into chamber 21 on movement of separation device 19 within tube10. Separation device 19 is comprised of separation shell 22 and plug24. Separation shell 22 has a first shell recess 25 disposed towardsfirst chamber 20 and second shell recess 26 disposed towards secondchamber 21; first shell recess 25 may contain a filter (not shown).Separation shell 19 also has first flange 27 and second flange 28, whichin the embodiment shown are non-planar curved surfaces that extend toand are in sliding engagement with inner wall 15 of tube 10, and form aneffective fluid tight seal therewith; flanges of other shapes may beused. While two flanges are shown, and are preferred, it is believedthat at least one flange is required. Plug 24 is located in second shellrecess 26. The inner surface 30 has a convoluted path formed in thesurface thereof which, in conjunction with the surface of plug 24, formsa channel (not shown, see FIG. 4) that is in fluid flow communicationbetween opposite ends of plug 24. Separation shell 19 is shown as havingan axial orifice 29 for flow of fluid.

The space between first flange 27 and second flange 28, either betweenthe separation device 19 and the inner wall 15 or the region in firstrecess 25, is used for monitoring of the separation process. Whileoptical monitoring of the process is a preferred method, other methodse.g. infrared and ultrasonic, may be used.

Plug 24 would normally be made from an elastomeric material, especiallya self-sealing elastomeric material. As will be apparent from thedisclosure herein, in one mode of operation, especially the embodimentshown in FIG. 2, a needle is inserted through second end cap 12 (viarecess 16), through plug 24 for the insertion of liquid into firstchamber 20. Plug 24 has additional requirements with respect operationof the method described herein, during movement of the separation device19 within tube 10.

The materials of construction of the end caps and plugs or stoppers inthe embodiments of FIG. 1, and FIG. 2 and other embodiments, willparticularly depend on the method of operation. End caps will normallybe relatively rigid plastic, depending on whether penetration by needlesis required. Plugs or stoppers may be rigid or elastomeric, includingself-sealing elastomeric, depending on whether a needle is passedthrough the plug prior to centrifugation thereby requiring self-sealingmaterial. The self-sealing materials referred to herein are known in theart of blood collection tubes.

FIG. 2 shows an embodiment that is the same as that shown in FIG. 1,except that tube 10 has only second end cap 12 i.e. first end cap 11 hasbeen replaced by using a tube having only one open end, at the locationof second end cap 12. End 31 is integral with the remainder of tube 10.In addition, second end cap 12 holds stopper 23 in position at the endof tube 10. Stopper 23 is shown as snugly fitting separation device 19,such that chamber 21 (not shown in FIG. 2 but shown elsewhere) hasbecome an incipient chamber.

FIG. 3 shows a separation device, generally indicated by 40; separationdevice 40 is the same as separation device 19, but shown in more detail.Separation device 40 has a separation shell 41 with plug 43. Plug 43 islocated in second axial recess 46, which is at the opposite end ofseparation shell 40 from first axial recess 45. A channel (not shown)with a convoluted path is located at the interface between plug 43 andthe surface of separation shell 40 that defines the shape of secondaxial recess 46. Access channel 47 is located in separation shell 40between first axial recess 45 and second axial recess 46.

Separation shell 40 also has first flange 48 and second flange 49. Eachof first flange 48 and second flange 49 are intended to contact theinner surface of a tube and to be in sliding engagement therewith, tothe extent that no significant amount of liquid will pass by firstflange 48 and second flange 49 and cause contamination of separatedphases.

FIG. 4 shows a plan view of the channel with a convoluted path locatedon separation shell 40 of FIG. 3, at the interface between second axialrecess 46 and the separation shell. The surface 60 of second axialrecess, generally indicated by 61, has central axial orifice 62,manifold 63 and channel 64. Channel 64 has entrance 65 and exit 66, andis shown as being a single continuous channel between entrance 65 andexit 66. However, in the embodiment shown, channel 64 has eightright-angled elbows so that channel 64 twists and turns around thesurface 60 of second axial recess 61. A convoluted path is thus formed,and the convoluted path has sections that are generally in each of aradial direction, an axial or longitudinal direction andcircumferentially oriented. It is believed that the path requiresaxially oriented sections with opposed directions of flow, andpreferably such that the longitudinal axis is substantially encircled,to inhibit reverse flow in the channel, as discussed hereinafter;radially oriented sections are believed to be less important withrespect to flow of fluid or inhibition thereof.

FIG. 5 shows a section of the separation device along the line 5--5 ofFIG. 4. Separation device 70 has a first flange 71 and a second flange72. First axial recess 73 is in fluid flow communication with axialorifice 74 that is located on the longitudinal axis of separation device70. Plug 75 in second axial recess 76 is shown in cross-section. Channel77 in plug 75 has a convoluted path, commencing with channel entrance 78which is in fluid flow communication with axial orifice 74. As shown inthe drawing, channel 77 proceeds from channel entrance 78 in an axialdirection, turns at right angles and proceeds circumferentially for adistance and then turns into an axial direction that is opposed to theaxial direction connected to channel entrance 78. Channel 77 is thenshown as proceeding further in a circumferential manner and then in anaxial direction.

FIG. 6 shows another embodiment of a separation device. Separationdevice 80 has first flange 81 and second flange 82, as well as firstaxial recess 83 and second axial recess 84. In this embodiment, there isno axial channel per se formed between first axial recess 83 and secondaxial recess 84, but rather opening 85. Opening 85 has insert plug 86therein, insert plug 86 being recessed into and seated with plug 87 insecond axial recess 84. Insert plug 86 has axial channel 88 located onthe longitudinal axis of separation device 80. Axial channel 88 isshowing as extending for the full length of insert plug 86, beforeproceeding through two right-angled bends to be axially oriented in theopposed direction and then in a radial direction. Axial channel 88 thenconnects with plug channel 89 formed at the surface of plug 87, andfinally exits at exit 90.

FIG. 7 shows an exploded view of the embodiment of FIG. 6. Separationdevice 80 has first axial recess 83 and second axial recess 84, withopening 85 therebetween. Opening 85 is adapted to accept plug 87. Insertplug 86 fits into and seats in plug recess 91 in plug 87. Insert plug 86has axial channel 88 located on the longitudinal axis of separationdevice 80. Axial channel 88 is showing as extending for the full lengthof insert plug 86, before proceeding through two right-angled bends tobe axially oriented in the opposed direction and then in a radialdirection. Plug channel 89 is formed in separation device 80 at secondaxial recess 84.

In operation, a sample of liquid having phases of differing densitiese.g. blood, is placed in the tube; the operation of the method of theinvention will generally be described herein with reference toseparation of blood into a cell fraction and a non-cellular fraction.The blood is inserted into first chamber 20. In the embodiment of FIG.1, this may be done by removing first end cap 11 and inserting theblood. However, for safety reasons, blood is normally drawn into firstchamber 20, as a consequence of having a vacuum inside first chamber 20,using a needle. This may be done by injection through first end cap 11and plug 13 directly into first chamber 20 in the embodiment of FIG. 1.Alternatively, for the embodiment of FIG. 2, blood is drawn in tochamber 20 through a needle inserted through second end cap 12, throughplug 24 and into chamber 20; in this embodiment, the material from whichplug 24 is fabricated must be selected so as to permit the needle topass through the plug under reasonable force and be self-sealing onwithdrawal of the needle, and to provide sufficient resistance to theprobe during movement of the separation device along the tube withoutdistending to plug the channel. Injection through first end cap 11 ispreferable as it overcomes potential contamination problems associatedwith withdrawal of the needle through second end cap 12 and drops ofblood becoming deposited in second chamber 21 or in recess 16 after theneedle is withdrawn; droplets in recess 16 would contaminate the probesubsequently inserted to obtain movement of the separation shell 19within tube 10 in a single-ended tube i.e. a tube with only one end cap,but not in a double-ended tube i.e a tube with end caps on both ends, asin the latter the needle is passed through one end cap and the probe ispassed through the other end cap.

The separation device is particularly intended for use in an axialcentrifuge e.g. an axial centrifuge of the type described in theaforementioned U.S. Pat. No. 4 828 716. The separation device is rotatedabout its longitudinal axis to effect phase separation. When separationis complete, the high viscosity, concentrated, clotted cells are locatednear the tube wall and the lower viscosity serum (and any air or othergases) are located closer to the longitudinal axis. A probe thenpenetrates second end cap 12 and contacts and is resisted by second plug24. Further force by the probe causes the separation device to movealong tube 10, thereby decreasing the volume of first chamber 20. Thisdecrease in volume results in the material located on the longitudinalaxis flowing through access channel 47, along the convoluted pathlocated at the interface between plug 24 and separation shell 19 andinto second chamber 21. Air or other gaseous matter is the first to flowinto second chamber 21, followed by serum. An optical sensor is locatedexterior to the tube and is able to monitor the separation device as itmoves along the tube. The sensor passes light through that part of shellrecess 25. When blood cells approach shell recess 26 and are detected,the movement of the probe, and hence the separation device 19, ceases,and thus the blood cells do not enter second chamber 21. The probe iswithdrawn while the tube is still being rotated about its axis, with theresult that the probe does not become contaminated by the sample in thetube. Thus, it is believed that the probe may be used on a subsequentsample without cross-contamination of samples.

The tube is made of an optically transparent material e.g. glass orSelar® polyamide, which is manufactured by E.I. du Pont de Nemours andCompany of Wilmington, Del. U.S.A. Other optically transparent materialsmay be used, prime requirements being acceptable transparency andsufficient strength to withstand the forces applied in a centrifugationprocess. In addition, the tube must be capable of retaining a vacuum, acapability of retention of vacuum for a period of about 2 years beingpreferred. Tubes or vials of acceptable properties are known and used inthe collection and processing of blood. The separator shell may bemoulded from thermoplastic or other polymers, a prime requirement beingthat the polymer not have adverse effects on the properties andcharacteristics of the blood and the components thereof. The separationdevice needs to be optically transparent, if optical means are to beused for the monitoring and control of the method of separation of theliquid into phases. Otherwise, a material suitable for the particularmonitoring method is required. In addition, the separation device needsto provide an adequate fluid seal against the side of the tube in whichit is located, and be capable of being fabricated into the shape of theseparation device. An example of a suitable material is polypropylene.

The material used in the fabrication of the plugs will depend inparticular on the tube being used. For a single ended tube, it isessential that a needle be able to penetrate through the plugs so thatliquid e.g. blood can be introduced into the first chamber; the materialneeds to be self-sealing on withdrawal of the needle and not core i.e.plug the needle with a portion of the plug. Subsequently, if a probe isused to move the separation device along the tube, then the material ofthe plug must be able to provide sufficient resistance to the probe toobtain movement of the separation device, while at the same time notcausing distortion or the like of the plug to the extent that thechannels required for fluid flow become blocked. Ethylene/vinyl acetatepolymer compositions have been found to be acceptable, including Elvax®250, 260, 450 and 550 polymer compositions available from E.I. du Pontde Nemours and Company, but other compositions will become apparent topersons skilled in the art. If a double ended tube is used, there is noneed for a needle to penetrate the plug, and the requirements on theplug are less stringent.

The end caps need to be made from a self-sealing material, especially aself-sealing elastomeric material. Examples of such materials are knownin the art.

The convoluted path of channel 64 is important with respect to the flowof material through the channel. It is preferable that fluid not flowback from second chamber 21 into first chamber 20 after the axialcentrifuging of the tube has ceased, but it is more important that fluidnot continue to flow, albeit intermittently, from first chamber 20 intosecond chamber 21. In particular, it is important that in-use handling,including inverting, laying on side, dropping, shaking and tipping ofthe tube, does not result in flow of fluid in either direction,especially not flow of the cell fraction from chamber 20 into chamber21. The convoluted path accomplishes has characteristic, when indimensions suitable for the fluid being separated. The channelpreferably has both a circumferentially-oriented section and alongitudinally-oriented section. As discussed above, at least onereversal of direction axially and a substantially complete encirclementof the longitudinal axis offset from that axis should be used to preventflow from sedimentation of cells, regardless of tube orientation, buttwo or more changes of axial direction are preferred; an axial spiralhas been found to give unacceptable results. In addition, because ahigher pressure is required to force concentrated, clotted cells throughthe flow channel than for serum, it is possible to provide a channel ofsufficiently small area and sufficient length to permit the flow ofserum but inhibit the flow of cell fractions.

The convoluted path of the channel is described herein as preferablylocated on the surface of a cone, primarily for reasons of ease ofmanufacture. However, the channel could be located on surfaces ofdifferent shape e.g. cylinders, spheres or the like, but such channelsmay be substantially more difficult to manufacture in a consistentmanner.

The separation shell and plugs are fabricated separately for ease ofmanufacture. In the embodiments in the drawings, the entire flow channelhas been shown to be fabricated in the surface of the separation shell,which is preferred for ease of manufacture but, in other embodiments, itcould be fabricated as part of the plug. As noted above, conical matingsurfaces, as shown, are preferred.

The separation device of the present invention has a minimal number ofindependent parts, resulting in few critical mating surfaces andconnections, for improved consistency and reliability from tube to tube.In addition, the separation device is of a passive design, with nomovable parts. The separation device has a longitudinally located axialchannel for effective separation of serum from blood cells, and providesmaximum serum yield with minimal air retention in the first chamber 20.The chambers are essentially free of sharp edges and discontinuoussurfaces, or the like, that might promote cell trauma or retention of aclot. The single flow channel is believed to be important, sincemultiple channels tend to permit cross-flow between chambers and resultin inferior separation. The channel should be of small cross-sectionalarea, especially so that only a small portion of the separated phase isretained within the channel. The flow path is long and convoluted ortortuous, resulting in a long flow distance within a relatively smallseparation device, which also maximizes the volume available within thechambers for blood component collection and storage.

A filter may be used in first shell recess 25 to filter fluid passingthrough that recess to the axial orifice. For example, platelets couldbe filtered from the blood fraction passing through the axial orifice.

It is understood that the tubes may contain anticoagulants or clotactivators, as is known in the art.

Although the tube and separation device have been described herein withparticular reference to axial centrifugation, at least some tubes andseparation devices described herein are also capable of being used inconventional centrifuges. It is to be understood, however, that theseparation device may not function in the manner described herein eventhough the tube containing the separation device is usable.

The present invention is illustrated by the following examples:

EXAMPLE I

To illustrate separation of blood into components using the separatordevice of the present invention, two samples of blood were collected byconventional means and then transferred into a single ended tube havinga separation device as illustrated herein. The plug in the separationdevice was fabricated from Elvax 550 ethylene/vinyl acetate copolymerand the separation device had centre line sampling as is illustrated.The blood was allowed to clot for one hour. The tubes were then placedin an axial centrifuge and, after the cellular and non-cellularcomponents had become ordered, the separation device was moved down thetube using a probe; the probe was stopped prior to the cellularcomponent entering the separation device. A sample of the non-cellularcomponent (serum) was removed and analyzed in the laboratory of theOttawa Civic Hospital, Ottawa, Ontario.

As a comparison, two samples of blood were taken using commerciallyavailable tubes viz. Becton Dickinson vacutainer tubes, and after beingallowed to clot for one hour were centrifuged in a conventional swingingbucket centrifuge. A sample of the non-cellular component (serum) wasremoved and analyzed at the same time as the above samples in thelaboratory of the Ottawa Civic Hospital, Ottawa, Ontario.

The blood was obtained from the same person, on the same day.

The results obtained were as follows:

                  TABLE I                                                         ______________________________________                                                    Run 1  Run 2    Run 3    Run 4                                    ______________________________________                                        Blood volume (mL)                                                                           8.2      8.5      8.3    8.5                                    Serum volume (mL)                                                                           2.9      2.9      3.5    3.6                                    Relative serum                                                                              61       59       80     79                                     yield (%)                                                                     Serum quality good     good     good   good                                   Serum colour  clear    clear    --     --                                     WBC (× 10.sup.6 /L)                                                                   0        0        0.1    0.1                                    Platelet count (× 10.sup.9 /L)                                                        5        6        4      4                                      RBC count (× 10.sup.12 /L)                                                            0        0        0      0                                      Hemoglobin (mg/%)                                                                           1        1        1      1                                      Sodium (mM/L) 146      145      146    145                                    Potassium (mM/L)                                                                            4.4      4.3      4.3    4.1                                    Chloride (mM/L)                                                                             107      108      107    107                                    Glucose (mM/L)                                                                              4.4      4.1      3.9    3.5                                    Urea (mM/L)   6.8      6.7      6.7    6.7                                    Creatinine (μM/L)                                                                        104      108      104    104                                    Urate (μM/L)                                                                             283      281      286    280                                    Calcium (mM/L)                                                                              2.4      2.4      2.37   2.34                                   Albumin (g/L) 43       43       43     43                                     Total Protein (g/L)                                                                         72       72       71     71                                     phosphate (mM/L)                                                                            1.05     1.05     1.06   0.97                                   ALT (Units/L) 24       23       22     24                                     AST (Units/L) 23       22       24     23                                     Alkaline phosphatase                                                                        89       89       89     89                                     (Units/L)                                                                     Cholesterol (mM/L)                                                                          5.2      5.4      5.2    5.2                                    Total bilirubin (μM/L)                                                                   10       10       10     9                                      Direct bilirubin (μM/L)                                                                  2        2        2      2                                      Gamma GT (Units/L)                                                                          23       24       24     23                                     LDH-L (Units/L)                                                                             153      142      142    155                                    Creatinine kinase                                                                           94       93       90     92                                     (Units/L)                                                                     Magnesium (mM/L)                                                                            0.89     0.88     0.89   0.88                                   Carbon dioxide (mM/L)                                                                       31       32       33     32                                     Triglycerides (mM/L)                                                                        1.75     1.75     1.70   1.71                                   ______________________________________                                         Note:                                                                         Runs 3 and 4 are the comparative runs.                                   

The values given in the above table, and the variation in the resultsobtained, are within normal tolerance variation for such tests. Thisshows that the separation device, tube and method of the invention giveeffective separation of blood components. The operation of the probe canbe, and has been, adjusted to give a higher serum yield.

We claim:
 1. A method of partitioning a pre-selected phase of a sampleof liquid having a plurality of phases of differing densities,comprising the steps of:(a) containing said sample of liquid in a firstchamber of a linear tube, said tube having a second chamber that isseparated from the first chamber by a separation device, said secondchamber being free of the liquid, said separation device slidablyengaging the interior surface of the tube in a fluid-tight manner andhaving an axial orifice on the longitudinal axis of the tube that is influid flow communication with a flow-restriction channel, saidflow-restriction channel being off-set from the longitudinal axis of thetube, said flow-restriction channel having a convoluted path with atleast two axially-oriented sections with opposed directions of fluidflow, said axial orifice being in fluid flow communication with thefirst chamber and said flow-restriction channel being in fluid flowcommunication with the second chamber; (b) ordering the phases of thesample concentrically by rotating the tube around its longitudinal axis;(c) while the phases are ordered, reducing the volume of the firstchamber by movement of the separation device within the tube, that phaseof the liquid located axially within the first chamber flowing into theaxial orifice and passing through the flow-restriction channel into thesecond chamber; and (d) deriving phase-separation information from thelocation of the interface between the phases and controlling thereduction of the volume of the first chamber on the basis of thephase-separation information.
 2. The method of claim 1 in which theflow-restriction channel permits flow of liquid from the first chamberto the second chamber during step (c) but restricts flow of liquid atother times.
 3. The method of claim 1 in which the flow-restrictionchannel is a single continuous channel.
 4. The method of claim 3 inwhich the second chamber is an incipient chamber that forms as theseparation device is moved along the tube.
 5. The method of claim 4 inwhich the single continuous channel substantially encircles thelongitudinal axis of the tube.
 6. The method of claim 3 in which theconvoluted path conforms to the surface of a cone.
 7. The method ofclaim 3 in which the tube is a single-ended tube, with an end cap ononly one end of the tube.
 8. The method of claim 3 in which the tube isa double-ended tube, with an end cap on both ends of the tube.
 9. Amethod of partitioning a pre-selected phase of a sample of liquid havinga plurality of phases of differing densities, comprising the stepsof:(a) containing said sample of liquid in a first chamber of a lineartube, said tube having a second chamber that is separated from the firstchamber by a separation device, said second chamber being free of theliquid, said separation device slidably engaging the interior surface ofthe tube in a fluid-tight manner and having an axial orifice on thelongitudinal axis of the tube that is in fluid flow communication with aflow-restriction channel, said flow-restriction channel being off-setfrom the longitudinal axis of the tube, said flow-restriction channelhaving a convoluted path with at least two axially-oriented sectionswith opposed directions of fluid flow, said axial orifice being in fluidflow communication with the first chamber and said flow-restrictionchannel being in fluid flow communication with the second chamber; and(b) ordering the phases of the sample by subjecting the tube tocentrifugal force.
 10. The method of claim 9 in which the flowrestriction channel is a single continuous channel.
 11. The method ofclaim 10 in which the tube is a single-ended tube, with an end cap ononly one end of the tube.
 12. The method of claim 10 in which the tubeis a double-ended tube, with an end cap on both ends of the tube.